1. Field of Invention
This invention pertains to an adhesive system for optical devices. More particularly, this invention pertains to fiber optical devices, such as those used for switching fiber optic cables, and securing optical components or elements in a housing such that misalignment of the components due to environmental changes is minimized.
2. Description of the Related Art
Fiber optic systems typically require fiber optic elements, such as switches and couplers, to perform the desired operations of the system. Because of this, it is common for a fiber optic system to include at least one fiber optic element. However, associated with the inclusion of fiber optic elements is the undesired characteristic of insertion loss. Insertion loss is the loss of signal power due to the insertion of a device into a transmission line. More particularly, an optical signal has greater signal power when it enters a fiber optic element than it does when it leaves the fiber optic element. Although, insertion loss is unavoidable when incorporating fiber optic elements into a fiber optic system, the displacement or misalignment of fiber optic elements, such as collimators and actuators, within the fiber optic element induces unnecessary insertion loss. The displacement or misalignment of fiber optic elements causes an optical signal to travel a path slightly altered from the designed signal path. The altered path prevents a receiving collimator from receiving a robust signal, and in extreme conditions, the receiving collimator receives no signal.
Fiber optic elements are typically secured within the housing of a fiber optic element by way of epoxy resin. Epoxy resin, commonly referred to as epoxy, is a flexible, usually thermosetting resin made by the copolymerization of an epoxide with another compound having two hydroxyl groups and is typically used for adhesives. Conventionally, a fiber optic element is secured within the housing of a fiber optic element by first inserting the element into a corresponding port that is defined by the housing. The port is sized slightly larger than the element and shares the same general shape of the element. After being inserted into the port, the element is aligned for designed operation. Epoxy is then applied around the outer surfaces of the element and the inner surfaces of the port such that a layer of epoxy is disposed between the element and the housing, thus securing the element within the housing. The epoxy is then cured by exposing the epoxy to the light from an ultraviolet wand. During the process of curing, the epoxy expands and contracts and displaces the corresponding fiber optic element from its designed position. The displaced element causes a corresponding optical signal to travel the previously discussed altered path. Additionally, epoxy expands and contracts in response to thermal variations. Therefore, exposure to thermal variation further displaces the fiber optic element.
Another limitation of conventional fiber optic elements is the difficulty they present regarding the application of epoxy. Once a fiber optic element is inserted into its corresponding port, the remaining space in which the epoxy is applied is very limited and difficult to access. This causes the application of the epoxy to be cumbersome and sometimes insufficient. Similarly, curing the epoxy that has been applied within the confined space offered by conventional elements is cumbersome and sometimes insufficient. Additionally, because conventional methods and devices confine the epoxy between an element and the housing of a fiber optic element, as the epoxy expands under thermal stimulation, it has potential to break the housing, the element, or both.
For example, U.S. Pat. No. 5,133,030, titled “Fiber Optic Switch,” issued to Lee on Jul. 21, 1992, discloses the conventional method of adhering optical elements. Lee discloses using an adhesive to secure optical fibers F1, F2 within a ferrule M by filling the gap between the fibers F1, F2 and the ferrule M with adhesive.